@noblegiraffe - my school is an international overseas one.
We do get quite a lot of 'joining the foreign legion' types - escaping the UK/elsewhere for personal reasons...not necessarily brilliant, dedicated teachers. Professional requirements are a bit woolly - notoriously American trained colleagues struggle with the British curriculum here in some subjects.
Then there are the 'gap yah' types who have somehow acquired a PGCSE or equivalent but just fancy a bit of fancy expat lifestyle for a year or two.
Then of course international teaching attracts 'rolling stones' anyway. Some of them are quite adept at moving on every 2 years before their first set of external results come out.
Then there are those who've taught nice biddable private school kids somewhere where education is hugely valued & parents appreciative. Ours are the kids of local bigwigs - politicians & CEOs. They require good classroom management (& amazing parent handling skills...). Ironically, for all where I am now is seen as a super posh school - the most successful colleagues tend to be battle hardened veterans of rough comprehensives.
Because everyone is on an initial fixed term 2 year contract - then renewed in yearly increments - there is little or no performance management.
If you pass your initial 3 months probation, but are a bit crap, nothing will be done about it until renewal time in January when you will be quietly told to start job hunting.
Also, we can't easily replace mid year. New staff have to be flown out, accommodation found, families found places at the school, visas & work permits arranged, etc etc. So easier for SLT to hang on to the warm bodies they have.
Plus appointment is by Skype. No one actually sees you teach till you get there & are in a classroom!
Disclaimer: vast majority of my colleagues are brilliant. But we do get the occasional disaster, & then we are very much lumbered with them.